The United States has deployed missile defence systems that will work with the Japanese and South Korean militaries to track a rocket North Korea says it will launch some time over an 18-day period beginning Monday.

Seoul: The United States has deployed missile defence systems that will work with the Japanese and South Korean militaries to track a rocket North Korea says it will launch some time over an 18-day period beginning Monday.

China, the North`s sole major ally but opposed to Pyongyang`s nuclear programme, appealed for calm.

North Korea has notified U.N. agencies it will launch a rocket carrying what it called an earth observation satellite some time between Feb. 8 and Feb. 25, triggering international opposition from governments that see it as a long-range missile test.

North Korea says it has a sovereign right to pursue a space programme. But it is barred under U.N. Security Council resolutions from using ballistic missile technology.

Coming so soon after North Korea`s fourth nuclear test, on Jan. 6, also barred by Security Council resolutions, a rocket launch would raise concern that it plans to fit nuclear warheads on its missiles, giving it the capability to strike South Korea, Japan and possibly the U.S. West Coast.

China has told North Korea that it does not want to see anything happen that could further raise tension, Chinese Foreign Minister Wang Yi said, describing "a serious situation", after a special envoy from China visited North Korea this week.

The United States has urged China to use its influence to rein in its neighbour.

Speaking to President Park Geun-hye, Chinese President Xi Jinping said he hoped all parties could bear in mind the broader picture of maintaining peace and stability on the peninsula, and "calmly deal with the present situation", China`s Foreign Ministry said.

"The peninsula cannot be nuclearised, and cannot have war or chaos," Xi said, also repeating a call for dialogue.

Japan`s Asahi Shimbun newspaper quoted Pentagon officials as saying that fuelling of the rocket appeared to have begun.It cited satellite footage showing increased activity around the missile launch and fuel storage areas, suggesting preparations for a launch could be completed within "a number of days" at the earliest.

A launch would draw fresh U.S. calls for tougher U.N. sanctions that are already under discussion in response to the nuclear test.

What would likely be an indigenous three-stage rocket will be tracked closely. South Korea and Japan have put their militaries on standby to shoot down the rocket, or its parts, if they go off course and threaten to crash on their territory.

"We will, as we always do, watch carefully if there`s a launch, track the launch, (and) have our missile defence assets positioned and ready," U.S. Defense Secretary Ashton Carter said on Thursday.

"We plan a lot about it. We and our close allies – the Japanese and the South Koreans - are ready for it."

South Korea has said its Aegis destroyers, its Green Pine anti-ballistic missile radar and early warning and control aircraft Peace Eye are ready.

A U.S. Navy spokesman confirmed the missile tracking ship USNS Howard O. Lorenzen arrived in Japan this week but declined to say if it was in response to the North`s planned launch.